<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    .box {
      width: 200px;
      height: 200px;
      background-color: aquamarine;
    }
  </style>
</head>

<body>
  <div id="app"></div>

  <script src="node_modules/@babel/standalone/babel.js"></script>
  <script src="node_modules/react/umd/react.development.js"></script>
  <script src="node_modules/react-dom/umd/react-dom.development.js"></script>
  
  <script type="text/babel">
    const element = ( 
      <div className="box"></div>  
        )
    ReactDOM.render(
      element,
      document.getElementById('app')
    )
  </script>
</body>

</html>